That part should be relatively straightforward - everything you need to know can be found in the emonLibDB zip file you download from this forum: EmonLibDB - Version 1.0.2 (Includes full documentation, example files.)
The hard part will probably be uploading it in the first place and then it will be to avoid updating it and losing your custom version if/when your emonPi2 decides to update itself, plus you’ll need to make changes in the emonHub configuration to pass the additional values forward to emonCMS.